Ekonomie 214 (Economics 214) Microeconomics Notes — Stellenbosch University (SU)

Ekonomie 214 (Economics 214) in the microeconomics sequence builds the tools you need to analyse how households, firms, and markets respond to incentives—prices, costs, constraints, and policy. The course typically combines core theory (demand and supply, utility and preferences, cost and production, market structures) with applied reasoning (efficiency, welfare, and market failures). These notes are written for students working within the Stellenbosch University (SU) Economics Course Notes collection and focus on microeconomic concepts commonly examined in Ekonomie 214 assessments, including quantitative problem-solving, interpretation of graphs, and rigorous argumentation.

1. Microeconomic Foundations: Preferences, Demand, and Consumer Choice (Ekonomie 214 Core Logic)

Microeconomics starts with the question: how do individuals choose when they face trade-offs? In Ekonomie 214, the “choice” model is usually formalised through preferences, budget constraints, and optimisation. Once you can derive an individual’s optimal choice, you can aggregate to market demand, interpret policy effects, and evaluate welfare.

1.1 Preferences, Utility, and the Meaning of “Rational Choice”

Most micro theory begins with assumptions about preferences. Even when you don’t explicitly prove them, exam questions often rely on them.

Common preference axioms include:

• Completeness: For any two bundles (A) and (B), the consumer can say either (A \succeq B) or (B \succeq A) (or both).
• Transitivity: If (A \succeq B) and (B \succeq C), then (A \succeq C).
• Continuity: Small changes in quantities don’t suddenly make a bundle irrelevant.
• Monotonicity (often used in basic demand): More of a good is never worse.

In graph-based exams, these assumptions justify:

• well-behaved indifference curves,
• the existence of an optimum where indifference curves are tangent to the budget line.

Example: Indifference Curves and “Tangency”

If indifference curves are convex, the consumer’s optimum typically occurs where:

• the budget line touches an indifference curve,
• and the marginal rate of substitution (MRS) equals the relative price.

This is the gateway to demand and welfare analysis.

1.2 Budget Constraint and Feasible Sets

A budget constraint sets the limit of what bundles can be purchased. With two goods (x) and (y), prices (p_x, p_y), and income (m):

[
p_x x + p_y y \le m.
]

• The budget line is the equality (p_x x + p_y y = m).
• The intercepts are:
  • (x)-intercept: (m/p_x)
  • (y)-intercept: (m/p_y)

In exams, you must be able to:

1. Write the budget equation.
2. Interpret intercepts.
3. Predict how the line shifts when income or prices change.

Scenario Consistency Check (Common Exam Style)

Suppose income increases from (m=R1000) to (m=R1200) while prices stay constant. Then the budget line shifts outward parallel to itself because the slope (-p_x/p_y) remains unchanged.

If instead (p_x) rises, the slope changes and the budget line rotates around the (y)-intercept.

1.3 Marginal Utility, MRS, and the Condition for Optimal Choice

Under standard assumptions, utility is maximised subject to the budget constraint. The first-order condition typically reduces to:

[
\text{MRS}_{xy} = \frac{p_x}{p_y}.
]

Where:

• (\text{MRS}_{xy} = \frac{MU_x}{MU_y}),
• meaning: the consumer is willing to trade (x) for (y) at a rate equal to their market trade-off.

Why this Matters for Micro Exam Questions

Many test questions ask you not only to compute but to explain directionality:

• If (p_x) increases, why does (x) consumption fall?
• Can substitution effects dominate?
• When might demand not fall? (Inferior goods and unusual preferences.)

1.4 Deriving Demand: Marshallian Demand and the Role of Income Effects

Demand is usually represented as (x(p_x, p_y, m)). When prices change, two key channels explain total effects:

• Substitution effect: change in relative price alters the optimal bundle along indifference curves.
• Income effect: change in purchasing power alters demand depending on whether the good is normal/inferior.

This decomposition underpins most welfare and policy interpretation.

Normal vs Inferior Goods

• Normal good: income effect is positive; (x) rises when income rises.
• Inferior good: income effect is negative; (x) falls when income rises.

Example: Inferior Good Demand with a Price Change

If a good is inferior, the income effect can partially offset the substitution effect. With a sufficiently strong inferior effect, demand may be less responsive or theoretically could even show “non-standard” behaviour (though for many standard models with convex preferences, price still typically reduces demand for normal goods).

1.5 Compensated Demand and Slutsky Decomposition (Exam-Grade)

The Slutsky identity connects the change in Marshallian demand to substitution and income effects:

[
\frac{\partial x}{\partial p_x} = \frac{\partial h_x}{\partial p_x} – x \frac{\partial x}{\partial m},
]

where:

• (h_x(p_x,p_y,\bar{m})) is compensated (Hicksian) demand keeping utility constant.

Interpretation:

• (\frac{\partial h_x}{\partial p_x}) is the substitution effect.
• (- x \frac{\partial x}{\partial m}) is the income effect, scaled by the initial consumption (x).

Practical Exam Approach

When asked “is the substitution effect always negative?”:

• Under standard convexity conditions, the substitution effect is negative for own-price: when (p_x) rises, compensated demand for (x) falls.

When asked “could the total effect be positive?”:

• Only if the income effect is strong enough (possible with inferior goods).

1.6 Market Demand Aggregation

For micro applications, you aggregate individual demands. If there are (N) consumers with identical preferences but different incomes (m_i), market demand at prices ((p_x,p_y)) is:

[
X_d = \sum_{i=1}^N x_i(p_x,p_y,m_i).
]

If a course includes quantitative market analysis, typical tasks are:

• compute changes in aggregate quantity demanded under price changes,
• interpret elasticity of demand,
• explain incidence of taxes using consumer and producer responses.

1.7 Elasticity: The Bridge from Theory to Policy

Elasticity measures responsiveness. For demand with respect to price:

[
E_d = \frac{\partial x}{\partial p} \cdot \frac{p}{x}.
]

• If (|E_d|>1): demand is price elastic.
• If (|E_d|<1): price inelastic.

Similarly, cross-price elasticity:

[
E_{xy} = \frac{\partial x}{\partial p_y} \cdot \frac{p_y}{x}.
]

• (E_{xy}>0) suggests substitutes.
• (E_{xy}<0) suggests complements.

Example: Policy Interpretation

If a government imposes a tax on a good:

• consumers pay more when demand is inelastic,
• firms bear more when supply is more elastic.

Elasticities are the quantitative core behind incidence.

2. Producer Theory: Production, Costs, and Supply (From Marginal Cost to Market Outcomes)

After consumer choice, Ekonomie 214 typically moves to how firms produce and decide outputs. Producer theory gives you demand for inputs, cost curves, and ultimately supply (or equilibrium conditions in markets).

2.1 Production Functions and Isoquants

A production function describes the relationship between inputs and output. For a firm using inputs (K) (capital) and (L) (labour):

[
q = f(K,L).
]

• The isoquant is the set of input bundles that produce the same output.
• Isoquants slope downward in (K)-(L) space if labour and capital substitute.

Key properties used in exam problems:

• Diminishing marginal returns when relevant.
• Convexity of isoquants implies diminishing rate of technical substitution.

2.2 Marginal Product and Diminishing Returns

Marginal product of labour:

[
MP_L = \frac{\partial f(K,L)}{\partial L}.
]

Under diminishing returns, as labour increases holding capital fixed, (MP_L) eventually falls.

Example: Simple Numeric Marginal Product Interpretation

If:

• At (L=1), (MP_L=10),
• At (L=2), (MP_L=7),
• At (L=3), (MP_L=4),

then adding more labour yields smaller extra output—diminishing returns. This is crucial for why cost curves behave as they do.

2.3 Cost Minimisation and the Cost Function

A firm chooses (K) and (L) to minimise cost for producing (q). If input prices are (w) (wage) and (r) (rent of capital), cost is:

[
C(q)=\min_{K,L} { wL + rK : f(K,L)\ge q}.
]

Cost function yields:

• Total cost (C(q)),
• Average cost (AC(q)=\frac{C(q)}{q}),
• Marginal cost (MC(q)=\frac{dC(q)}{dq}) (or discrete analogue).

2.4 Short-Run vs Long-Run Costs

Short run: at least one input is fixed (e.g., capital (K=\bar{K})). Long run: all inputs are variable.

• In the short run, there are fixed costs (F) and variable costs (VC(q)):
  [
  C(q)=F+VC(q).
  ]

• Total cost:

  • (FC(q)=F) constant,
  • (VC(q)) rises with output.

In exams, you must link these to curve shapes:

• (AVC) typically U-shaped due to diminishing returns and eventual increases in marginal cost.
• (MC) intersects both (AVC) and (AC) at their minima.

2.5 Profit Maximisation and Supply

A competitive firm takes output price (p) as given and maximises profit:

[
\pi(q)=pq – C(q).
]

FOC (continuous setting):

[
\frac{d\pi}{dq}=p – MC(q)=0 \Rightarrow p=MC(q).
]

So, in competitive markets:

• The firm supplies output where (p=MC) above shutdown conditions.

Shutdown in short run:

• if (p<AVC), the firm minimises losses by producing (q=0).

2.6 Discrete Output Example: Constructing a Supply Schedule

Often exams use tables with output levels and marginal costs. Example structure:

Output (q)	Total Cost (C(q))	Marginal Cost (MC)
0	0	—
1	50	50
2	95	45
3	135	40
4	175	40
5	225	50

If market price (p=45):

• produce where (MC \le p) (and next marginal cost would exceed price).
• Here, firm may choose (q=2) depending on whether (p) equals exact marginal steps and shutdown based on AVC.

This style appears across quantitative assessments because it tests:

• understanding of profit comparison,
• logic of choosing the highest profit output.

2.7 Elasticities of Supply and Long-Run Adjustments

Supply elasticity depends on:

• how quickly firms can adjust,

• availability of technology and capital reconfiguration,

• flexibility of input use.

• Short-run supply can be less elastic (fixed capital).

• Long-run supply tends to be more elastic if firms can enter/exit and reallocate resources.

Policy Relevance: Tax Incidence

Tax incidence depends on relative elasticities:

• more inelastic side pays more tax burden.

You often see questions on the effect of taxes on:

• consumer price vs producer price,
• deadweight loss.

Your job is to compute welfare changes and justify directional conclusions.

3. Market Structures, Competitive Equilibrium, and Welfare Analysis (Efficiency, Taxes, and Market Failures)

This section develops how markets reach equilibrium and how to measure efficiency. Ekonomie 214 microeconomics typically expects fluency in:

• competitive equilibrium,
• consumer and producer surplus,
• welfare effects of price controls and taxes,
• monopoly outcomes and deadweight loss.

3.1 Competitive Equilibrium: Graphical and Algebraic Conditions

In a competitive market:

• consumers choose quantities demanded based on utility maximisation,
• firms choose quantities supplied based on profit maximisation.

Equilibrium occurs when:

[
Q_d(p)=Q_s(p).
]

At equilibrium:

• price clears the market,
• quantity is determined by intersection of demand and supply.

Producer and Consumer Surplus

• Consumer surplus (CS): area under demand curve above price.
• Producer surplus (PS): area above supply (marginal cost) curve below price.

Total surplus (TS) is:

[
TS = CS + PS.
]

Competitive markets maximise total surplus under ideal conditions (complete markets, no externalities, no market power, etc.).

3.2 Welfare with Taxes: Deadweight Loss and Incidence

Consider a per-unit tax (t) imposed on buyers or sellers. In a simple diagram:

• the demand side effectively sees higher price,
• the supply side receives lower net price.

Let:

• consumers pay (p_c),
• producers receive (p_p),
• tax wedge (t = p_c – p_p).

Equilibrium changes:

• quantity falls from (Q^*) to (Q^{tax}),
• part of surplus becomes government revenue,
• the remainder is deadweight loss.

Deadweight Loss Logic

Deadweight loss arises because trades with valuation above marginal cost no longer occur due to the tax wedge.

Graphically:

• DWL is the “triangle” between supply and demand created by tax-induced reduction in quantity.

Incidence Formula Using Elasticities (Conceptual)

Even if the tax is levied on producers, consumers may bear much of the burden if demand is more inelastic.

To solve incidence quantitatively, you often use:

• supply and demand elasticities at equilibrium,
• linear approximations if curves are linear.

3.3 Welfare with Price Controls: Ceilings and Floors

Price ceilings (e.g., rent controls) and floors (e.g., minimum wage analogues) create distortions when binding.

Price Ceiling Example Structure

• If ceiling (p_{max}) is below equilibrium price:
  • quantity demanded (Q_d) rises,
  • quantity supplied (Q_s) falls,
  • shortage occurs.

Efficiency effects:

• some trades that should occur (between (Q_s) and (Q_d)) do not happen.
• Total surplus decreases.

You may also discuss secondary markets, rationing, and non-price allocation mechanisms if the syllabus touches on real-world deviations.

3.4 Monopoly and Market Power: Output Choice and Pricing

If a firm is a monopoly:

• it chooses quantity to maximise profit given demand.

Profit:

[
\pi(q)=p(q)q – C(q).
]

FOC in terms of marginal revenue (MR):

[
MR(q)=MC(q).
]

Since monopoly faces downward-sloping demand:

• marginal revenue lies below demand,
• monopoly chooses (q_M) where (MR=MC),
• sets price (p_M) from the demand curve at (q_M).

Welfare Comparison to Perfect Competition

Monopoly typically yields:

• higher price (p_M > p_C),
• lower quantity (q_M < q_C),
• deadweight loss from underproduction relative to the efficient competitive output.

However, monopoly can sometimes create dynamic efficiency arguments (innovation), though those are policy arguments rather than static welfare results.

3.5 Monopoly vs Perfect Competition: A Quantitative Welfare Template

A classic exam pattern:

1. Given demand and marginal cost, compute (q_M) from (MR=MC).
2. Compute (p_M) from the inverse demand (p(q)).
3. Compare to competitive equilibrium where (p=MC).
4. Compute:
   • consumer surplus,
   • producer surplus,
   • total surplus,
   • deadweight loss.

To be exam-ready, practice calculating areas under linear demand curves and interpreting intercepts.

Linear Demand with Constant Marginal Cost

Assume:

• demand: (p=a-bq),

• marginal cost: (MC=c) constant (so supply is horizontal at (c)).

• Competitive equilibrium:
  [
  p=c \Rightarrow c=a-bq_C \Rightarrow q_C=\frac{a-c}{b}.
  ]

• Monopoly:
  monopoly revenue: (TR=pq=(a-bq)q=a q – b q^2),
  [
  MR = a – 2bq.
  ]
  Set (MR=MC):
  [
  a-2bq_M=c \Rightarrow q_M=\frac{a-c}{2b}.
  ]
  So monopoly output is half of competitive output in this setup. The prices then follow accordingly.

This template appears frequently because it tests both algebra and welfare.

3.6 Externalities: When Markets Fail

A central microeconomics topic is externalities—situations where private costs or benefits differ from social costs or benefits.

• Negative externality (e.g., pollution): the marginal social cost (MSC) exceeds marginal private cost (MPC).
• Positive externality (e.g., education): marginal social benefit (MSB) exceeds marginal private benefit (MPB).

Efficient output equates:
[
MSB = MSC,
]
while private equilibrium equates:
[
MPB = MPC,
]
leading to under- or over-production.

Example Framework for Policy Instruments

• Pigouvian taxes: impose tax equal to marginal external cost to shift incentives.
• Subsidies: subsidise marginal external benefit.
• Tradable permits: allow efficient distribution of responsibilities.

Even if a particular exam focuses more on diagrams, the logic must be correct to earn full marks.

3.7 Asymmetric Information (If Included): Adverse Selection Intuition

Some Ekonomie 214 curricula include a brief segment on information problems. If so, the key logic is:

• Adverse selection: when sellers have private information about quality, leading to market breakdown or quality distortion.
• Signalling: informed parties take actions to reveal information (e.g., warranties, education).
• Screening: uninformed parties design contracts to sort types.

If your exam question includes an “explain” component, you must:

• specify the information asymmetry,
• show how it changes incentives,
• describe equilibrium outcome and potential remedies.

4. General Equilibrium Basics, Comparative Statics, and Applied Problem-Solving (Systems Thinking for Ekonomie 214)

As micro theory advances, you are expected to connect partial equilibrium intuition to general equilibrium or at least to multi-market reasoning. Even when the course doesn’t formally test general equilibrium, comparative statics and policy reasoning rely on systematic thinking.

4.1 From Partial to General Reasoning

Partial equilibrium analysis:

• focuses on one market,
• treats other markets as fixed.

General equilibrium analysis:

• considers how changes propagate through multiple markets via income effects and factor markets.

For Ekonomie 214, even if full general equilibrium is not required, exam questions often test:

• whether you correctly include indirect effects like income changes.

Example: A Tax on a Good with Substitutes

If the price of good (x) rises:

• substitution reduces consumption of (x),
• but income falls in real terms,
• which affects demand for other goods (y).

So if (y) is a normal good:

• demand for (y) decreases due to income effect,
• while substitution might increase or decrease depending on whether goods are substitutes or complements.

4.2 Comparative Statics: Direction of Effects

Comparative statics is the study of how equilibrium changes when parameters shift.

Key tools:

• derivatives,
• elasticity-based approximations,
• Slutsky decomposition,
• substitution/income effect logic.

Case: Price Rise in a Linear Model

Suppose demand: (Q_d = \alpha – \beta p) and supply: (Q_s = \gamma + \delta p).
Then equilibrium price is:

[
\alpha – \beta p = \gamma + \delta p \Rightarrow p=\frac{\alpha-\gamma}{\beta+\delta}.
]

If a parameter like (\alpha) increases (shifts demand up), then equilibrium price rises:

• because numerator increases,
• denominator unchanged.

This algebraic discipline earns points, especially when graphs are ambiguous.

4.3 Surplus Decomposition: Gains from Trade and Efficiency

Efficiency comparisons often use surplus decomposition.

If a market is efficient, the competitive equilibrium yields maximum total surplus under the assumptions. Taxes reduce total surplus because they:

• prevent marginal trades that create net benefits.

But exam questions sometimes ask:

• does total surplus decrease by “more” or “less” if the tax changes?
• how does elasticity change the deadweight loss?

A crucial concept:

• deadweight loss increases more when demand and supply are inelastic? Actually, DWL is larger when quantity reduction is large relative to the tax wedge; that depends on curvature/elasticities.

In linear approximations:

• deadweight loss is proportional to the square of the tax magnitude (for small taxes), under certain settings.

4.4 Transfers vs Distortions (A Common Exam Concept)

Not all welfare changes involve efficiency loss.

• A lump-sum transfer changes income but not relative prices; it can change who is better off without necessarily changing total surplus (depending on externality presence).
• A distortion (taxes, price controls, quotas) changes relative prices and generally causes deadweight loss.

So in answers:

• Distinguish between distributional effects and efficiency effects.
• Use correct language: “surplus redistribution” vs “allocative inefficiency.”

4.5 Consumer Welfare Measures: Equivalent Variation and Compensating Variation (If Covered)

Some micro courses include advanced welfare measures:

• compensating variation (CV): amount of money to compensate for price change so consumer attains original utility after change.
• equivalent variation (EV): amount of money equal to the price change effect measured relative to original prices/utilities.

Even when not heavily tested, understanding the concept helps interpret questions on welfare and policy.

For many exam settings, instructors may focus on:

• how to interpret CS changes as an approximation,
• why exact welfare depends on utility shape and the presence of income effects.

4.6 Quantitative Techniques: Solving for Equilibrium and Welfare in Practice

To be strong in Ekonomie 214 problem sets, practise a standard pipeline.

Standard Pipeline for a Market Policy Question

1. Write demand and supply equations (or read them from question).
2. Find baseline equilibrium:
   • solve (Q_d(p)=Q_s(p)) to get (p^) and (Q^).
3. Introduce policy:
   • tax wedge (t),
   • price ceiling/floor,
   • subsidy, etc.
4. Compute new equilibrium:
   • determine consumer price and producer price (if applicable).
5. Compute welfare:
   • consumer surplus,
   • producer surplus,
   • government revenue,
   • deadweight loss.

Example: Tax with Linear Curves (Template Calculations)

Assume:

• (Q_d = 100 – 2p),
• (Q_s = 20 + 2p).
  Baseline:
  [
  100 – 2p = 20 + 2p \Rightarrow 80 = 4p \Rightarrow p^=20.
  ]
  Then:
  [
  Q^ = 100 – 2(20)=60.
  ]

Now impose tax (t) per unit. With per-unit tax, if consumer price is (p_c) and producer price is (p_p=p_c – t), then:

• demand uses (p_c),
• supply uses (p_p).

Equations:
[
Q_d = 100 – 2p_c,\quad Q_s = 20 + 2(p_c – t).
]
Set equal:
[
100 – 2p_c = 20 + 2p_c – 2t
\Rightarrow 80 = 4p_c – 2t
\Rightarrow p_c = \frac{80+2t}{4}=20+\frac{t}{2}.
]
Then (p_p=p_c-t=20-\frac{t}{2}).
Quantity:
[
Q^{tax}=100-2p_c=100-2\left(20+\frac{t}{2}\right)=60-t.
]

Then compute:

• government revenue (= t \cdot Q^{tax} = t(60-t)),
• CS and PS using triangle/trapezoid areas depending on intercepts.

This method yields internally consistent numbers and reduces errors.

4.7 Linking Factor Markets to Output: Labour Demand and Supply (If Included)

Micro courses often connect firm decisions to labour markets:

• firms demand labour where (w = MPL) in simple models,
• competitive labour supply then determines wage.

If you are asked to interpret a labour market policy (e.g., minimum wages), you should:

• determine whether labour supply and demand slopes imply unemployment,
• discuss welfare effects and distribution.

5. Extensive Exam-Style Synthesis: Mastering Graphs, Algebra, and Argumentation in Ekonomie 214 (SU Micro)

This final section consolidates the skills that exams test most heavily: graph literacy, algebraic precision, and written economic reasoning. It also builds a bank of reusable frameworks for common question types.

5.1 Graph Literacy: Reading Curves, Slopes, and Intercepts

An Ekonomie 214 examiner typically expects you to interpret graphs quickly and correctly. Focus on:

• Slope meaning:
  • demand slope: how quantity responds to price,
  • supply slope: responsiveness of quantity to price,
  • indifference curve slope: trade-offs between goods.
• Tangency condition:
  • optimum where marginal rate of substitution equals price ratio.
• Intersection logic:
  • equilibrium where demand equals supply,
  • monopoly where marginal revenue equals marginal cost.

Common Graph Pitfalls

• Confusing total surplus with consumer surplus.
• Treating a shift in demand as movement along demand (incorrect line usage).
• Using the wrong price for consumer vs producer when tax is present.

5.2 Algebraic Precision: Keep Units and Relationships Consistent

Where possible:

• keep consistent notation: (p_c) and (p_p) for consumer/producer prices under tax,
• keep domains consistent: taxes affect feasible prices differently,
• avoid sign errors in derivatives.

A Unit Discipline Example

If demand is in units per week and prices are in rand per unit, then:

• marginal revenue computed from (TR=p(q)\cdot q) should have consistent units,
• welfare area computations should reflect currency areas.

5.3 Step-by-Step Written Reasoning: How to Score High

Written answers should show the examiner you can reason economically. A good structure is:

1. State the relevant equilibrium condition (e.g., (p=MC) for competitive output; (MR=MC) for monopoly).
2. Identify the effect of the policy change (tax wedge, price control, subsidy, externality).
3. Determine directional impacts on price, quantity, and welfare components.
4. Conclude with efficiency and distribution statements (who gains, who loses, and why).

Example Answer Skeleton: Tax on a Good

• “A per-unit tax creates a wedge between consumer price (p_c) and producer price (p_p): (p_c=p_p+t).”
• “Equilibrium quantity falls because demand depends on (p_c) and supply depends on (p_p).”
• “Government revenue equals (t \cdot Q^{tax}).”
• “Total surplus falls by the deadweight loss, the lost trades between the efficient and post-tax quantities.”
• “Incidence depends on elasticities: with inelastic demand, consumers bear a larger share.”

5.4 Decision Rules for Firm Closure, Entry, and Market Exit

Even if not the most “math heavy” topic, Ekonomie 214 questions often test conceptual understanding of market dynamics.

In competitive markets:

• A firm exits in the long run if it cannot earn zero economic profit.
• In the short run, shutdown occurs if price falls below AVC.

Shutdown vs Exit

• Shutdown (short run): (p < AVC) → produce zero.
• Exit (long run): economic profit negative → leave the market.

In graphs:

• shutdown is based on (AVC),
• exit based on (AC).

5.5 Monopoly Pricing: Why MR Sits Below Demand

Monopoly pricing often appears as:

• find equilibrium output and price,
• compute deadweight loss.

Key reasoning line:

• because the monopolist must lower price to sell more units, marginal revenue is less than price.

In linear demand (p=a-bq):

• (MR = a – 2bq),
• hence MR intercept equals price intercept but slope is twice as steep.

5.6 Welfare Diagrams: Deadweight Loss Calculation Intuition

DWL is often calculated as a triangle under linear curves. The exam-grade habit:

• identify the efficient quantity (Q^*),
• identify the policy quantity (Q^{policy}),
• identify the wedge between marginal benefit and marginal cost at the margins where trades cease,
• compute DWL as ( \frac{1}{2} \times \text{base} \times \text{height} ).

Height can be:

• tax per unit (t) in a simple setting,
• marginal gap due to externalities.

5.7 Worked Mini-Case Sets (Synthesis Practice)

Mini-Case A: Competitive Equilibrium and Tax Deadweight Loss

Given linear demand and supply, use:

• equilibrium computation,
• tax wedge model,
• DWL triangular area.

Checklist:

• compute baseline (p^, Q^),
• compute post-tax (p_c, p_p, Q^{tax}),
• compute CS, PS via triangles,
• government revenue via rectangle,
• verify that:
  [
  \text{baseline total surplus} = \text{post-tax total surplus} + \text{DWL}.
  ]

Mini-Case B: Monopoly Output with Constant MC

Use template:

• (p=a-bq), (MC=c),
• competitive (q_C=\frac{a-c}{b}),
• monopoly (q_M=\frac{a-c}{2b}),
• compare welfare areas.

Even without explicit numbers, the ratio results help interpret the shape of welfare losses.

Mini-Case C: Externality and Efficient Quantity

If a negative externality implies:

• private marginal cost (MPC),
• social marginal cost (MSC=MPC+ \text{marginal external cost}).

Then:

• market produces where (p= M P C),
• socially efficient output where (p=MSC) (or (MSB=MSC) in positive/negative general form).

In an exam, if the question asks “what policy corrects the market?”:

• state the Pigouvian tax amount equals marginal external cost at the efficient quantity.

5.8 South African University Context: How SU Courses Often Test Micro

At South African universities (including SU), microeconomics exams typically mix:

• calculus and algebra for optimisation,
• diagram interpretation,
• applied welfare and policy reasoning.

Students often perform better when they can switch between:

• a written explanation (why demand falls),
• a mathematical step (MRS equals price ratio, (MR=MC)),
• a graphical statement (tangency, equilibrium intersection, triangles for DWL).

Practise combining these in single answers:

• “Because (p=MC) in perfect competition, equilibrium is efficient—tax creates a wedge causing DWL.”

This “linking phrase” is a common scoring mechanism: it shows you understand the economic logic, not only the computation.

5.9 Final Revision Strategy: What to Practise Repeatedly

For Ekonomie 214, the fastest route to marks is repetition on the same core patterns:

1. Demand with substitution and income effects:
   • identify normal/inferior,
   • predict direction with price changes.
2. Cost curves and firm decisions:
   • derive profit maximisation condition,
   • apply shutdown rule.
3. Welfare with taxes and externalities:
   • compute surplus components,
   • explain incidence and efficiency.
4. Monopoly vs competition:
   • (MR=MC), output below competitive, DWL present.
5. Market equilibrium with policy shifts:
   • compute new equilibrium and interpret results.

Use past-question style practice: write down the equilibrium condition first, then solve, then interpret welfare.

5.10 Consistent Economic Language for High Marks

Finally, examiners reward precision in terminology:

• “Efficient” typically means maximising total surplus, or equating marginal social benefit and marginal social cost.
• “Allocatively inefficient” implies distortion of marginal trades due to market failure or policy.
• “Incidence” refers to distribution of tax burden between consumers and producers, not only who pays it legally.
• “Deadweight loss” is due to reduced quantity relative to efficient outcome.
• “Transfers” redistribute surplus without necessarily changing total surplus.

Using this language reliably helps your reasoning look coherent and correct even when calculations are complex.

Summary of Key Takeaways

• Consumer theory: maximise utility subject to the budget constraint; price changes create substitution and income effects.
• Producer theory: minimise cost for given output; competitive supply derives from (p=MC) with shutdown based on (AVC).
• Market structures: competition yields efficiency under standard assumptions; monopoly restricts output where (MR=MC), creating DWL.
• Welfare and policy: taxes and externalities create wedges between private and social marginal values; DWL measures lost efficiency.
• Exam performance: master equilibrium conditions, graph interpretation, and stepwise computation with coherent economic explanations.

These notes should equip you to handle the typical range of Ekonomie 214 microeconomics question styles: derivations, graph-based welfare analysis, and policy reasoning grounded in marginal concepts.